Multi-element jet engine noise suppressor nozzle systems have presented considerable design problems in the past. They have been difficult to fabricate and their overall girth, length, and base area have in some cases restricted takeoff roll attitudes and have produced aerodynamic drag penalties. Further, multi-element jet noise suppressors have tended to be ineffective at lower jet velocities common with the lower power settings for turbojet engines as well as the entire range of power settings for high bypass ratio engines.
In the prior art, internal ventilation for jet noise control has been attempted. A search of the patent literature illustrates a number of systems in which the ambient air has been introduced into a jet engine nozzle for the purpose of noise suppression. U.S. Pat. No. 3,910,375 illustrates a jet engine silencer in which ambient air is permitted to flow from the exterior of the nozzle into a central body. The entry direction is such to cause substantial loss in the volume of airflow due to friction and flow turbulence. The air is caused to mix with the exhaust gases externally of the nozzle. This arrangement provides for only a small internal ventilation area, and a relatively complicated actuation system is required to operate the flaps in the central body externally of the nozzle to permit airflow therethrough.
U.S. Pat. No. 3,039,560 discloses a silencer in which inlets of air ducts are spaced around the periphery of the nozzle. The air ducts extend radially inwardly so that the gas flows therearound and out of the nozzle. Outlets of the air ducts are in the same plane as the outlet of the nozzle from which the exhaust gases flow.
U.S. Pat. No. 3,613,826 illustrates a jet engine silencer having ambient air intake vents spaced around the nozzle periphery. Orientatable tubular elements extend from the vents into the nozzle and are terminated substantially inwardly of the nozzle discharge end.
In U.S. Pat. No. 3,650,348 jet exhaust gas exits through round tubes, and ambient air enters the nozzle through peripheral openings and passes around the gas exhaust tubes, the gas and air being mixed at the downstream end of the nozzle.
In U.S. Pat. No. 2,944,624 jet engine gas is exhausted through elliptical tubes having tapered troughs open on one side to permit the entry of the ambient air into the individual nozzle members, the air and gas exhaust being mixed immediately externally of the end of the nozzle members.
The following additional patents, found in the search, disclose noise suppressors and jet deflecting devices for use with jet engines:
U.S. Pat. No. 2,793,493 PA1 U.S. Pat. No. 2,799,990 PA1 U.S. Pat. No. 2,812,636 PA1 U.S. Pat. No. 3,084,507 PA1 U.S. Pat. No. 3,174,282 PA1 U.S. Pat. No. 3,572,463 PA1 U.S. Pat. No. 3,618,701 PA1 U.S. Pat. No. 4,052,847 PA1 Australian No. 165,369 PA1 Great Britain No. 894,299